Photoelectrophoretic imaging method employing a chromogenic reaction

ABSTRACT

An imaging system wherein imaging particles are electrophoretically deposited imagewise on a receiving layer in response to a light image. The imaging particles comprise a chromogenic material and the receiving layer comprises a coreactant therefor. The chromogenic co-reactants are reacted on the receiving layer to form a colored well fixed, final image.

United States Patent [1 Wells et al.

[ PHOTOELECTROPHORETIC IMAGING METHOD EMPLOYING A CHROMOGENIC REACTION [75] Inventors: John B. Wells, Rochester; Joseph Mammino, Penfield, both of NY.

[73] Assignee: Xerox Corporation, Rochester, NY.

[22] Filed: Jan. 4, 1973 [21] Appl. No.: 321,103

[52] U.S. Cl 96/1.3, 96/1 PE, 96/49, 96/1.2, 96/48 R, 96/1.5, 96/48 HD, 96/1.8,

96/50 R, 204/181 PE [51] Int. Cl.... G03g 5/00, G03g 13/00, G03g 17/00 [58] Field of Search 96/1.3, 1.2, 1 PE, 1 R; 204/181 PE; 117/37 LE [56] References Cited UNITED STATES PATENTS 3,003,891 10/1961 Albrecht 96/1 R X 3,329,590 7/1967 Renfrew..... 3,373,019 3/1968 Bixby 96/1 R 3,386,379 6/1968 Gundlach et al. 96/1.2 X 3,471,309 10/1969 Thompson 117/37 LE X [4 1 Nov. 19,1974

3,511,650 5/1970 Shely et al. 96/1 R 3,562,248 2/1971 Jones et al. 204/181 PE X 3,622,368 11/1971 Okuno et al. 117/37 LE 3,658,675 4/1972 Jones et a1. 204/181 PE 3,705,797 12/1972 Mihajlov et al. 96/1 PE 3,716,360 2/1973 Fukushima 117/37 LE X T879009 10/1970 Stademayer et al. 1 17/37 LE T887,027 6/1971 Chechak 96/l.2

FOREIGN PATENTS OR APPLICATIONS 43-10,271 4/1968 Japan 96/1.2

Primary Examiner-Roland E. Martin, Jr.

Assistant Examiner-John R. Miller, Jr.

Attorney, Agent, or Firm-James J. Ralabate; David C. Petre; Richard A. Tomlin [5 7 ABSTRACT An imaging system wherein imaging particles are electrophoretically deposited imagewise on a receiving layer in response to a light image. The imaging particles comprise a chromogenic material and the receiving layer comprises a co-reactant therefor. The chromogenic co-reactants are reacted on the receiving layer to form a colored well fixed, final image.

9 Claims, 1 Drawing Figure PATENTEL zmv 91914 I 3.849.132

' Tim m (g PI-IOTOELECTROPI-IORETIC IMAGING METHOD EMPLOYING A CHROMOGENIC REACTION This invention relates in general to an imaging system and more particularly to an electrophoretic imaging system.

In one form of electrophoretic imaging, generally referred" to as photoelectrophoretic imaging, colored photosensitive particles are suspended in an insulating carrier liquid. This suspension is then placed between at least two electrodes, subjected to a potential difference and exposed to a light image. Ordinarily, in carrying out the process, the imaging suspension is placed on a transparent electrically conductive support in the form of a thin film and exposure is made through the transparent support while a second generally cylindrically shaped biased electrode is rolled across this suspension. Although not wishing to be bound by any theory or mechanism, it is currently believed that the particles hear an initial charge once suspended in the liquid carrier which causes them to be attracted to the transparent base electrode upon application of a potential difference. Upon exposure, the particles change polarity by exchanging charge with the base electrode so that the exposed particles migrate to the second or roller electrode thereby forming images on each of the electrodes by particle subtraction, each image being complementary, one to the other. An extensive and detailed description of the photoelectrophoretic imaging techniques as generally referred to may be found in US. Pat. Nos. 3,383,993; 3,384,488; 3,384,565 and 3,384,566 which are hereby incorporated by reference.

Other electrophoretic imaging processes have been developed in which an imaging suspension comprising a mixture of electrically photosensitive particles and inert particles dispersed in a carrier liquid is placed in an electrical field between electrodes, at least one of which is transparent, and exposed to imagewise electromagnetic radiation through the transparent electrode. While the above steps are being completed, images are formed by particle migration on both electrodes. The images are formed by the migration of the photosensitive particles or migration of the inert particles depending upon the polarity of the applied field as described in copending application Ser. No. 104,388, filed Jan. 6, 1971, entitled Imaging Process now US. Pat. No. 3,772,013 and assigned to the same assignee herein. For the purposes of the present invention, it is the image formed by the migration of the inert imaging particles which is of interest. Said application is incorporated herein by reference. The term inert particles" refers to those particles which will not, when suspended alone, respond significantly to the levels of radiation used. The inert particles may comprise conductive, semi-conductive and insulating materials and may themselves be electrically photosensitive. Where an electrically photosensitive material is used as the inert material, the inert material should have a response about one-tenth or less that of the response of the photosensitive material to insure complete separation of the photosensitive material from the inert photosensitive material. That is, it should require at least times as much exposure to the radiation used to migrate. Since the inert particles useful in this process may comprise, for example, brilliantly colored thermoplastic materials, high-quality, full-color images may be produced by transferring three or more monochromatic images formed by this process to a common substrate in register.

An electrophoretic imaging system has also been developed wherein finely-divided particles dispersed inan insulating liquid are placed between a photoconductive electrode and a second electrode. The photoconductive electrode is exposed to a pattern of radiation to which it responds while a field is applied across the suspension between the photoconductive electrode and the second electrode. The photoconductive electrode causes those particles which are within interaction range of the illuminated parts of said electrode to take on the same sign of charge as the photoconductive electrode and be repelled by it. These repelled particles migrate to the surface of the second electrode in image configuration forming a negative image on the surface of the second electrode and leaving a positive image behind.

The particles which may be dispersed in the insulating liquid may be insulating, semi-conductive or conductive and may comprise two or more components. Since it is essential that the particles be capable of accepting and retaining charge injectedfrom the photoconductive electrode, it has been found desirable that the surface of the particles be made of a material which has a bulk resistivity of at least 10 ohm-cm. and preferably l0 ohm-cm. or greater. There is no known upper limit of operability in that particulate dyed plastics having resistivities of greater than 10 ohm-cm. have been found to work very well.

To obtain the greatest advantages of this process where a uniform dispersion of particles in a liquid is used, the dispersed particles are initially forced to the surface of the photoconductive electrode by application of field. For example, where the photoconductive electrode is held at a positive potential with respect to the second electrode during imaging, the suspension is first charged negatively by, for example, a negative corona discharge which causes the particles to take on a negative charge. When the suspension is placed on the positive photoconductive electrode the particles are drawn to the surface of thephotoconductive electrode leaving a relatively thick layer of particle-free liquid between the particles and the second electrode. When the photoconductor is exposed to radiation to which it is sensitive, particles which are adjiacent to illuminated areas of the photoconductive electrode exchange charge with the photoconductive electrode and migrate through the liquid to the second electrode. When precharging is used initially, only liquid contacts the second electrode and, therefore, background is measurably improved. In other words, the only particles which contact the second electrode are those which have migrated there as a result of charge exchange with the photoconductive electrode.

This electrophoretic imaging process is described in copending application Ser. No. 104,389, filed Jan. 6, 197 l, entitled Imaging Process and is assigned to the same assignee as herein now abandoned in favor of continuation application Ser. No. 290,618, filed Sept. 20, 1972. This application is incorporated herein by reference. To produce a full color image with thisprocess, three or more monochromatic images are formed corresponding to color separation images, each in a pri mary color, and are transferred in register to a single substrate resulting in full color synthesis.

After the above described exposure and particle migration steps are completed in electrophoretic imaging processes of the kind described above, the electrodes are separated and the carrier liquid is removed such as by evaporation. This leaves images on one or both electrodes made up of selectively deposited photosensitive particles. The images are, at this time, fragile and easily damaged. The carrier liquid may contain a small proportion of a dissolved wax or other binder which, on evaporation of the carrier liquid, serves to bind the particles together. However, if more than a very small amount of binder material is dissolved, undesirable interference with the imaging process takes place.

It has been suggested that a transparent binder material be sprayed over the images to form a protective coating. While, when carefully done, these techniques will protect the image, the image may be damaged during application of the protective material. Other methods of fixing images use heat or solvent tackifiable layers which are rendered tacky and contacted to the image, such as those disclosed in copending applications Ser. Nos. 459,860, filed May 28, 1965; and 677,706 and 677,707, both filed Oct. 24, 1967 all now abandoned. However, these techniques also suffer from defects of the kind mentioned above.

Additionally, when it is desired to transfer the image from an electrode to a receiving sheet, the danger of damaging an unfixed image is high.

Moreover, colored, electrically photosensitive particles are quite expensive and must be used in relatively high concentrations to give good quality images. The intensities of the electric field and the light source required to effect imaging generally increase as the concentration of photosensitive particles in the imaging suspension increases. Great savings in complex apparatus and power consumption would be possible by decreasing required intensities of the electric field and the light source. Accordingly, it would be desirable to have a photoelectrophoretic imaging system capable of utilizing relatively low-cost photoconductive particles in relatively low concentrations.

it is, therefore, an object of this invention to provide an electrophoretic imaging system which overcomes the above-noted disadvantages.

It is another object of this invention to provide a novel imaging system.

it is another object of this invention to provide a rela tively simple imaging system.

It is another object of this invention to provide an imaging system capable of providing high-quality, wellfixed images.

It is another object of this invention to provide an electrophoretic imaging system capable of producing dense, high-quality images utilizing imaging suspensions containing relatively low concentrations of migrating particles.

It is another object of this invention to provide a photoelectrophoretic imaging system capable of utilizing low-cost electrically photosensitive imaging particles.

The above and other objects are accomplished in accordance with this invention which provides, in an electrophoretic imaging process wherein a layer of an imaging suspension comprising imaging particles suspended in an insulating liquid is placed between at least two electrodes maintained at different electric potentials, and the imaging particles are caused to migrate in image configuration toward at least one of said electrodes in response to a light image, the improvement which comprises:

employing imaging particles comprising a chromogenic material;

providing an image receiving layer comprising a coreactant for the chromogenic material of the imaging particles;

causing the imaging particles to migrate to the image receiving layer in imaging configuration; and

chromogenically reacting the chromogenic material of the imaging particles with the co-reactant of the receiving layer.

The final image is produced according to the present invention by chromogenically reacting the chromogenic material contained in the imaging particles on a reactive receiving layer. Depending upon the selection of materials, the chromogenic reaction can take place upon contact with the receiving layer or after the appli cation of activating energy, a solvent, or an additional reactant. But in any event, because the image is formed by a chromogenic reaction between the imaging particles and the receiving layer, a well-fixed, durable image is obtained.

The present invention will become more apparent from the ensuing discussion, particularly when taken in conjunction with the following drawing, wherein:

The FIGURE is a side sectional view of a simple, exemplary photoelectrophoretic imaging system for carrying out the process of the present invention.

Referring now to the FIGURE, an imaging suspension, generally designated 1, comprising electrically photosensitive imaging particles 3 in insulating carrier liquid 5 is coated on a substrate, generally designated 7. In this exemplary instance, the substrate 7 comprises glass layer 8 with a thin transparent layer 9 of tin oxide on its surface. Tin oxide coated glass of this kind is available commercially as NESA glass. A second electrode, generally designated 10, is made up of a conductive core 11 having an insulating layer 12 and an outer layer 13. Where the process is used to form an image at the second electrode, layer 13 may be made up of a substrate, such as paper or film, coated with a chromogenic co-reactant for a chromogenic material contained in the particles 3. Insulating layer 12 may be deleted if desired, particularly when layer 13 is relatively insulating.

Alternatively, suspension 1 can be placed on surface 13. A source of DC potential is connected to surface 9 and ground. The opposite terminal of potential source 19 is connected through switch 20 to conductive core 11.

- In operation, switch 20 is closed and roller electrode 10 is caused to traverse the suspension while the suspension is exposed to imagewise electromagnetic radiation 21. As roller 10 traverses the suspension, particles 3, which have been exposed to radiation to which they are sensitive, exchange charge with surface 9, are repelled by it, and migrate to surface 13 in image configuration. On completion of the traverse by roller 10, an image made up of the particles is found adhering to surface 13, the image being of opposite image sense from the original. That is, light areas on the original show up as imaged areas on surface 13.

The carrier for the imaging suspension may comprise any suitable insulating material which may be a liquid or it may be a solid which may be converted to a liquid by heat or solvent application at the time of particle migration. Typical insulating materials include decane, dodecane, N-tetradecane, kerosine, molten paraffin, molten eicosane, molten beeswax or other molten thermoplastic material, mineral oil, silicone oils such as dimethyl polysiloxane and fluorinated hydrocarbons. Solvents such as Sohio 3440 and 3454 (kerosene fractions available from Standard Oil of Ohio) are preferred because they are effective insulators, suitably volatile, and relatively inert.

The concentration of photosensitive particles may vary over a wide range. Typically, from about 2 parts to about 150 parts by weight of particles based on 100 parts by weight liquid is used. The range permissible will vary depending on how stable the suspension can be made, operating conditions and other factors. Lower concentrations reduce field and light intensity requirements, but result in images of decreased density. Preferably, from about 5 parts to about 40 parts by weight particles based on 100 parts by weight liquid is used. It is desirable to use electrically photosensitive particles which are relatively small in size because smaller particles produce more stable suspensions with the carrier liquid and are capable of producing images of higher resolution than would be possible with particles of larger sizes. Thus, it is preferred that the photoresponsive particles be less than about one micron in size although particles of up to five microns may readily be used.

The photosensitive imaging particles employed may be of a single component of two or more components. For example, a particle may consist wholly of a material such as zinc oxide which is both electrically photosensitive and chromogenically reactive with materials such as vinylidene chloride polymers or copolymers. In other instances, it may be desirable to use a particle employing zinc oxide, as the electrically photosensitive component, in combination with a chromogenic material such as a diazo color coupler which is chromogenically reactive with a diazo compound. Additionally, a colored, electrically photosensitive pigment may be coated or impregnated with a chromogenic material which, when chromogenically reacted, can change or intensify the color of the image. By thus enabling color intensification, it is possible to decrease the concentra tion of the photosensitive material in the imaging suspension.

Although it is preferred to use a conductive electrode and an electrode having an insulating surface, the system will operate with both electrodes having insulating surfaces or both electrodes being conductive. It is preferred, however,-to use a conductive electrode which allows ease of charge exchange with'the photosensitive particles and an electrode having an insulating layer which retards charge exchange preventing particle oscillation in the system and to help support the relatively high fields used in the process. A potential of at least about 300 volts per mil across the imaging suspension is required to form images. Much higher voltages are routinely used however, for example, in the apparatus as shown in the drawing from 2,000 to 7,0000 volts may be used. To further increase field strength across the imaging suspension, the electrodes are brought into virtual contact, with a gap of up to about one mil being preferred. Larger spacings cause loss of resolution.

In one embodiment of the present invention, particles of zinc oxide are dispersed in an insulating carrier liquid and coated on a transparent conductive substrate. The imaging suspension is exposed to imagewise radiation, to which the particles are sensitive, through the transparent electrode, while the free surface of the imaging suspension is traversed with a roller electrode having a conductive core and a reactive receiving surface comprising a copolymer of vinylidene chloride and acrylonitrile coated on a white paper substrate. The zinc oxide particles deposit on the resin surface in image configuration forming a white-on-white image since the zinc oxide and paper are white and the resin is clear. Heating causes the image to become brown or black by reaction of the zinc oxide with the resin. The heat also fixes the image and forms a hard, glossy surface film.

Preferably, the resin is present on the surface of the opposing electrode for a number of reasons. First, an extremely low background image can be formed on this electrode if the electrically photosensitive particles are initially drawn to the surface of the transparent electrode resulting in the formation of a clear liquid layer over the particles which helps keep nonmigrating particles from contacting the resin. Further, opaque substrates such as paper may be used. However, if desired, the resin layer can be placed on the surface of the transparent conductive electrode. This is possible be cause the resin is transparent and capable of effecting sufficient charge exchange when used as a relatively thin film. a positive-to-positive image can thus be formed.

According to this embodiment, the particles may be of a single component or of two or more components. For example, the electrically photosensitive particle may have a colorant layer overlying a photosensitive core to alter photosensitive response. Further, the photosensitive particle may be a mixture of two or more electrically photosensitive materials to broaden spectral response. Typical electrically photosensitive particles and materials for use therein are listed in the above patent, US. Pat. No. 3,383,993.

The chromogenic reaction which. occurs between the zinc oxide and the copolymer of vinylidene chloride described above is a decomposition and carbonization reaction which occurs at relatively low temperatures. For example, after the zinc oxide is deposited imagewise on the copolymer coated sheet, a sharp, dark image is formed by passing the sheet carrying the image through a conventional Xerox 914 Copier fuser station. In place of a heated wire, warm air, a heated platen, an infrared lamp or any other suitable heating device may be used.

A wide variety of chromogenic co-reactants may be used in place of the copolymer mentioned above. Typical of the polymeric materials which can be used in the above reaction are: vinyl chloride polymers, vinylidene chloride polymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-vinyl acetate copolymers, vinyl chloride-ethylene copolymers, halogenated rubbers, halogenated styrene polymers, halogenated polyesters, halogenated olefin polymers, etc. Typical of the monomeric materials which may be employed along with a suitable binder such as polyvinyl acetate, polyvinyl alcohol, ethyl cellulose, cellulose acetate, alkyd resins, polyamides, polyacrylates, etc., are: halogenated compounds such as carbon tetrabromide, bromoform, iodoform, hexabromoethane, hexachloroethane; halogenated vegetable oils such as linseed oil, soybean oil, cotton seed oil, etc.; halogenated fatty acids such as stearic acid, lauric acid, etc. Additionally, materials such as halogenated paraffin wax may be employed. These and other suitable materials are set forth in US. Pat. Nos. to S. B. Elliot, 2,712,916; 2,772,158; 2,772,159; and 2,789,053.

Copolymers of vinylidene chloride and acrylonitrile are preferred because of the permanence and contrast of the image produced by the reaction.

In another embodiment of the present invention, the photosensitive particles are used to carry chromogenic materials, other than the photosensitive material itself, to the surface of a receiver layer. In this instance also, the receiver layer contains a material which is chromogenically reactive with the chromogenic material contained in the photosensitive particles. It is thus possible according to this embodiment to form either monoor polychromatic images. That is, by proper selection of at least two different chromogenic reactant pairs capable of forming different colors, and by proper selection or sensitization of the photosensitive particles such that they are sensitive to light of at least two corresponding colors, it is possible to illuminate the imaging suspension with a polychromatic light image to achieve a polychromatic image upon effecting the chromogenic reaction in accordance with the present invention. While there should be correspondence between the colors to which the particles are sensitive and the colors produced by the chromogenic reactions, these colors need not be the same unless this is desired.

As an example of a monochromatic method according to this embodiment, a diazo sheet is used on or as the blocking layer and the photosensitive particles are coated with the color coupler for the reactant on the sheet. It is preferred to coat the more transparent reactant on the photosensitive particle to minimize light absorption of the layer thereby more efficiently using the light available to render the photoresponsive component responsive.

Typical co-reactants for the diazo process include any of the diazo compounds and color couplers known to the art.

The diazo compounds may be used as such or in the form of their stabilized double salts such as a diazonium zinc chloride, cadmium chloride or stannous chloride double salt.

Representative of specific diazo compounds which may be suitably employed in the present invention include 1-diazo-4-diethylaminobenzene; l-diazo-2,5- diethoxybenzoylaminobenzene; l-diazo-2,5-dibutoxybenzolaminobenzene; 1-diazo-4-tolylmercapto- 2,5-diethoxybenzene; 1-diazo-2,5-dimethoxy- 1 -ptolylmercapto-benzene; l-diazo-3 -ethoxy-4- diethylaminobenzene; l-diaz-4-(N-hydroxyethyl-N- methyl )-aminobenzene; 1-diazo-4-n-propylamino-3-npropoxybenzene; p-diazo-diphenylamine; l-diazo-2- chloro-4-(dihydroxyethyl)-aminobenzene; 1-diazo-4- dimethyl-aminobenzene; l-diazo-4-dihydroxypropylaminobenzene; 1 -diazo-3-methyl-4- dimethylaminobenzene; l-diazo-2-carboxy-4- dimethylaminobenzene; and 1-diazo-4- diamylaminobenzene.

Representative of specific diazonium salts are: 4-benzoylamino-2,5-diethoxybenzene-1-diazonium chloride zinc chloride double salt; 4-diethylaminobenzene-l-diazonium chloride zinc chloride double salt; 4-diphenylaminobenzene diazonium chloride double salt; or a diazo oxide such as that derived from 2- amino-4-chloro-5-nitrophenol.

2. Acids such as oxalic acid, and

Representative of the couplers which can be employed are those such as, for example, phloroglucinol: 1 ,3,5-trihydorxy-2-methylbenzene; l ,5-dihydroxy-2- methylbenzene; o-hydroxydiphenyl; lhydroxynaphthalene, cyanacetanilide; 4- (acetoacetamido)-benzene sulfonamide; resorcinol monoacetate; 1-acetylamino-2-naphthol-5-sulfonic acid; p-methyl-N-phenylpyrazolone; 3-methylpyrazolone; 2,4xylenol; thiobarbituric acid; 3,4- dihydroxytoluene; 1,S-dihydroxynaphthalene; acetyl acetanilide; and 2,3-dihydroxynaphthalene. A list of other suitable couplers may be found in the article by Van de Grirten, Photographic Journal, volume 928 (1952).

The diazo compound or coupler may also be dis solved or dispersed in a polymeric binder. The binder may be softened by heat or solvent to permit the chromogenic reaction to occur and to fix the image. Treatment with a weak base such as ammonia may be requried to effect the chromogenic reaction.

The preferred electrically photosensitive particle for carrying the color coupler is zinc oxide because it is white and does not mask the color formed and because it is not strongly acidic or basic thereby not interferring with the color forming reaction. However, any other suitable photosensitive material such as CdSSe, Se, CdS, T10 antracene, or powdered polyvinyl carbazole and powdered polyvinyl carbazole-charge transfer complexes can be used.

In addition to the diazo-type chromogenic coreactants there are a wide variety of other colorforming materials which can be employed according to the present invention. Representative chromogenic coreactant pairs are listed in the following Table I. Generally, those materials listed in column A would be more suitable for use as a component of the electrically photosensitive particles and those materials listed in column B would be more suitable for use as a component of the image receiving member. However, it will be obvious to those skilled in the art that this preferred order may be reversed in many cases.

1. Compounds splitting ofi sullur inorganic and organic salts or soaps such as dithiooxamide,thioof iron, copper, silver, mercury, acctamide and p phenyllead, nickel, cobalt and cadmium erredlthiourea. such as copper stearate, silver nitrate, silver stearate, silver behenate, silver palmitatc, mercury stearate, lead acetate, lead stearate, lead myristate, nickel acetate, nickel steerate, cobalt stearate, cadmium stearate and lead benzyl rncreaptide.

Compounds that are sensitive to changes in the pH-value, e.g. leueomalachlte green, leucornethyi green, leucofuchine and leucolissamalonic acid.

mine green. 3. Oxldrzmg agents such as All compounds changing color on benzoyl peroxide, and tetraoxidation, e.g., pchloroaniline,

chloroquinone. methyl-p-aminophenol sulfate, N, N 'xiirnethyl-ophenylenediamine, antipyrine, pyragallol, pyrocatech01 and 4-meth0xy-1-naphthol.

Silver salts such as silver nitrate and silver behenate. gold salts such as gold chloride and gold stearate, triazolium compounds such as 2,3- diphenylnaphtho-[l,2l-trlazolium chloride and 2 phenyl-3-(o-carboxyphenyl)-naplitho-[1,Zl-triazolium chloride, tetrazollum compounds such as 2,5-diphenyl-3-(o-carboxyphenyl) 2,1 3.4tetrazoliumch1oride and 2, 5-diphenyl-3 p-methoxyphenyl)-2,l,3,4tetrazoliumchloride, ieucophthalocyanines such as Phthalogene Blue 113 (Farben fabrlken Bayer AG, Leverkusen, W. Germany).

4. 1-phcnyl-3-pyrazolidinone and derivatives such as l-phenyl- 4-methyl-3pyrazolidinone, and 1-(p-tolyl)-5-phenyl-3- pyrazolidlnone.

Table |Continued 5. 8-hydroxy-1,2,3,4 tetrahydroquinoline and derivatives.

7. Compounds containing an active methylene group such as N,N-dimethylbenzamide and N-methylacetamide.

8. Amines such as p-phenylenediamine, m-phenylenediamine and dlethanolamine.

I). Nitroso derivatives, 0.1;. N- nitrosodiphcnylamine, pnitrosodimethylaniline and l-nitrosoQ-naphtholu 10. Triazene compounds such as 1,3-diphenyl-triazene:

Inorganic and organic salts or soaps of iron, copper, silver, gold, cobalt and cadmium such as iron (III) chloride, iron (III) stearate, iron (II) sulfate, iron (II) stearate, copper (II) chloride, copper (II) stearate, silver nitrate. silver behenate and cobalt (II) chloride.

Oxidizing agents such as potassium dicthromate and ammonium molyb- Inorganic and organic salts or soaps of iron, copper, silver, gold, mer cury, nickel, cobalt, cadmium, cerium and tin, e.g. iron (III) stearate, iron (III) chloride, iron (II) chloride, iron (II) sulfate, iron (II) stearate, copper (II) sulfate, copper (II) chloride, copper (II) stearate, silver nitrate, silver stearate, silver behenate, gold (III) chloride, gold stearate, mercury stearate, nickel stearate, cerium (IV) stearate and tin (II) chloride.

Oxidizing agents such as potassium dichromate, ammonium molybdate, ammonium vanadate, and quinone derivatives such as tetrachloroquinone.

Nitroso compounds such as p-nitrosodimethylaniline and N-nitrosodiphenylamine.

-bromo-2-amino-thiazoles, e.g. 2- ethylamino-4-phenyl-5-bromothiazole and 2 diphenylamino 4 phenyl-fi bromothiazole.

Aromatic aldehydes and ketones,

e.g. tetrachloroquinine, IA-naphthoquinone, 2-chloronaphthoquinone, S-chlorovanillin, p-dimethylamino-benzaldehyde and 2,4-dinitro-benzaldehyde.

Aromatic hydroxy compounds, e.g. pyrogallol, gallic acid, methyl-p aminophenol sulfate, and 4- methoxy-bnephthol.

Metal salts, e.g. iron (II) sulfate and cobalt acetate.

Amines, cg. 2,5'diaminotoluene and benzylaniline.

Coupling agents for diazotype printing, e.g. 3-hydroxy-2-naphthanilide and 3-hydroxy-N-2-naphthyI-Z-naphthamide.

11. Aromatic amines and aromatic amino-hydroxy compounds, e.g. I-amino-Z-naphthol, 8-hydroxy-quinolinc, p-phenylenediamine, and m-phenylenediamine.

l2. Nitro compounds, e.g. 2

nitrochloroaniline, l-chloro- 2-nitro-4-diethyl sulfamoylbenzene and dinitroresorcinol.

i3. Compounds that, on heating set free alkali, e.g. those described in United Kingdom Patent Specification 983,363, filed May 8, 1961, by Nashua Corporation and alkaline compounds, e.g. diethanolamine, tetramethylguanidine. pphenylenediamine, and triethyl amine.

Sulfur-containing compounds, e.g. sodium sulfide, sodium tn'thionate, thioacetamide and thiourea. I

Silver salts, cg. silver nitrate, silver behenate, silver stearate, gold salts, e.g. gold (III) chloride and gold stearate.

Mercury salts, e.g. mercury behenate.

Caddmium salts, e.g. cadmium chlooxidizing compounds, e.g. iron (III) stearate. copper (II) chloride. copper (II) stearate, cerium (IV) sulfate. ammonium vanadate. sodium bromate, potassium dichromate acid.

Compounds that change in color when the pH changes, e.g. the leucoform of p-nitro-phenol, phenolphthalein, bromothymol blue. chlorophenol red, bromo cresol purple, oxonol dyes and 1,2,33- tetra-hydro-t-[2-(3-methyl-2-benzo thiazolinylidene)-ethylidene]- irplnItghylium-tctrachloroferrate Mixtures of a diazonium salt and a coupler, cg. the combination of pdiethvlarninobenzene diazoniumtetrzifluoroborate and phloroglu- CIIIO Ill An important factor to consider in the choice of which material is used as a component of the electrically photosensitive particles is the degree to which the photosensitivity or spectral response of the particles may be altered. This consideration becomes especially significant when it is desired to form polychromatic images, i.e., where a polychromatic light imageis used to cause migration of particles capable of forming twoor more different colors which correspond to the colors in the light image.

While the FIGURE and the above discussion illustrate the mechanism of the present invention with relation to forming images by the migration of electrically photosensitive imaging particles upon exposure to a light image in the presence of an electric field, it is to be understood that the invention applies equally to the migration of inert particles in an electric field in response to a light image as is discussed above and in said application Ser. Nos. 104,388 and 104,389. Inert particles are caused to migrate to a receiving layer in response to a light image, not by direct excitation by the light, but by charge transfer from a photoconductive layer on one of the electrodes or from photoconductive plarticles maintained in suspension with the inert partic es.

Thus, the method of the present invention can be em ployed with equal facility in imaging systems of the kind described in said Ser. No. 104,388 wherein at least one of the electrodes is transparent and the imaging suspension comprises electrically photosensitive particles in addition to the imaging particles, which according to this system are themselves inert to sensitization by light of the magnitude employed, and the step of causing the imaging particles to migrate to the image receiving layer in image configuration includes exposing the imaging suspension to a light image through the transparent electrode.

With equal facility, the process of the present invention can be employed in imaging systems of the kind disclosed in said Ser. NoilO4,389, wh erin at least one of the electrodes comprises a photoconductive layer which is in contact with said imaging suspension, and said imaging particles are inert to sensitization by light of the magnitude employed, and the step of causing the imaging particles to migrate to the image receiving layer in image configuration includes exposing the imaging photoconductive layer on said one electrode to a light image.

Where the process of the present invention is em ployed in systems of the type where migration of inert imaging particles is caused in response to a light image, the term inert is used to define the degree of electrical photosensitivity of the particles as discussed above and not their chromogenic reactivity. An inert particle can consist wholly of a chromogenic material as those defined above, or it can comprise a chromogenic material in combination with suitable binders or other materials which can be used to modify the electrical or physical properties of the imaging particles. The photoelectrically-inert, chromogenic materials which are detailed above, are equally suitable for use in inert imaging particles. Upon migration of the imaging particles to the image receiving layer comprising a co-reactant for the chromogenic material of the imaging particles, the chromogenic materials of the imaging particles and the co-reactant of the receiving layer are reacted in the same manner as described above for the embodiment EXAMPLE I An imaging suspension is prepared by dispersing approximately 40 parts of Photox 85 zinc oxide available from New Jersey Zinc Co., with about 01 part Rose Bengal DPI dye sensitizer, available from Eastman Chemicals, in about 100 parts of Sohio 3440 kerosene fraction available from Standard Oil of Ohio. The imaging suspension is coated onto the conductive surface of 4% inch square NESA glass plate to a thickness of about 6 mirons. The conductive surface of the plate is' connected to ground and the positive terminal of a source of 7000 volts DC. The negative terminal is connected through a switch to the conductive core of a 2 /2 inch diameter roller having a polyurethane blocking layer. A sheet of Xerox 100 bond paper is coated with Saran F242L, a copolymer of vinylidene chloride and acylonitrile available from Dow Chemical Co., by applying a 10 percent solution of the copolymer in methylene chloride using a No. 10 wire draw-down rod. The thickness of the copolymer layer when dry is about 5 microns. This sheet is wrapped around the roller electrode copolymer side out.

The roller is rolled under moderate pressure across the imaging suspension at a rate of about 2 inches per second, with potential supplied while the imaging suspension is exposed to an image through the NESA plate. The light image is obtained using a 500 watt quartz iodine lamp source to illuminate a black and white silver halide negative transparency, the image being projected by a lens through the NESA plate. On completion of roller traverse, a barely discernible positive image of ZnO particles is found adhering to the copolymer layer. The roller is then exposed to heat from a radiant heater capable of heating the coated paper surface to about 375F. for a few seconds. A dark brown-to-black image is formed by a combination of decomposition and carbonization of the copolymer layer in areas in which the zinc oxide is a contact. This image resists abrasion and handling. To destroy the image, it is necessary to destroy the copolymer layer.

EXAMPLE [I In this Example, the procedure of Example I is repeated, except that the polymer layer is placed on the injection electrode and the image is formed by nonmigrating particles.

The copolymer layer is formed on a 1 mil Mylar (polyethylene terephthalate) sheet instead of the Xerox 100 bond paper as in Example I. The sheet is placed on the NESA glass plate and the imaging suspension coated on the copolymer. The blocking roller electrode has a sheet of plain Xerox 100 bond paper on its surface. The roller traverse is made as in Example I. A second roller traverse is made to further remove unwanted particles from the copolymer layer. The image bearing sheet is then heated as in Example I forming a dark, brown-to-black image. This image is compared to the image formed in Example I. The image is characterized by slightly higher background than the image formed in Example I but the images are equally durable. Of course, the image formed in this Example is a negative image corresponding to the original negative transparency.

EXAMPLE III The procedure of Example I is repeated, except that the copolymer layer consists of VYNS, a copolymer containing percent vinyl chloride and 10 percent vinyl acetate available from Union Carbide Corporation. The copolymer is applied to a one mil sheet of polysulfone film from a 10 percent solution of the copolymer in methyl ethyl ketone to yield a coating having a dry thickness of 6 microns. The image formed is a dark brown-to-black. It is found that the formation of the image in this Example requires slightly longer heating than was required in Examples I and II and is suitable for transparency projection applications.

EXAMPLE IV In this experiment, diazo images are formed. The rol' ler electrode has a sheet of 85g/m tracing paper coated with a layer comprising 1 part of 2,5-diethoxy-4- benzoylamino-benzene-l-diazonium chloride zinc chloride double salt and 5 parts of a polyamide resin on its surface. The polyamide resin is obtained by condensing linoleic acid and ethylene diamine in accordance with US. Pat. No. 2,379,413. A polyamide resin of this type, Versamid 950, is available from General Mills, Kankakee, Illinois. The zinc oxide particles are coated with a color coupler for the above coated sheet as follows: about 1 part of 3,5-diethoxy phenol is dissolved in parts of methanol; 4 parts of zinc oxide are added to this solution; and the zinc oxide, thus coated with the coupler, is filtered and dried. The coated zinc oxide particles are dispersed in Sohio 3440 kerosene fraction as in Example I. About 20 parts of coated zinc oxide particles are dispersed in 100 parts by weight carrier liquid. The imaging process is carried EXAMPLE V The procedure of Example IV is repeated, this time using 4-dimethylamino benzene diazonium chloride zinc chloride double salt in the coating on the tracing paper and phloroglucide as the coating on the zinc oxide particles. Similar good results are achieved in forming the violet-to-black image.

EXAMPLE VI The procedure of Example IV is again repeated, but this time employing 3-chloro-4-pyrolidino benzene diazonium borofluoride salt as the diazo compound in the coating on the tracing paper, and 2,7-dihydroxy naphthalene as the color coupler coated on the aim oxide particles. Similar good results are achieved in forming a red-to-violet image.

EXAMPLE VII The procedure of Example IV is again repeated, but

this time l-diazo-2,5-dibutoxy benzoylamino benzene is employed in the coating on the tracing paper and phloroglucinol is employed as the coating on the zinc oxide particles. Similar good results are achieved in forming a brown-to-voilet image. I Although specific components and proportions have been described in the above Examples, other suitable materials, as listed above, may be used with similar re sults. In addition, other materials may be added to the various layers or imaging suspension to synergize, enhance or otherwise modify their properties. For example, the particles may exhibit a fatigue effect which allows exposure to imagewise radiation prior to field application.

EXAMPLE VIII In this example, the roller electrode contains a sheet thereon of 85 g/m tracing paper coated with a layer comprising about 1 part of silver behenate and parts of the polyamide resin employed in Example IV on its surface. Zinc oxide particles are coated with a compound capable of splitting off sulfur under color reaction conditions for the above coated sheet as follows: about 1 part of dithiooxamide is dissolved in 100 parts of methanol; 4 parts of zinc oxide are added to this solution and the zinc oxide thus coated with dithiooxamide is filtered and dried. The coated zinc oxide particles are dispersed in Sohio 3440 kerosene fraction as in Example I employing about parts of coated zinc oxide particles in 100 parts by weight carrier liquid. The imaging process is carried out as in Example I providing a positive image on the surface of the silver behenate coated sheet. The sheet bearing the image is then heated to fix the image and cause reaction to take place providing a black image.

EXAMPLE Ix In this example, the roller electrode contains a sheet thereon of 85 g/m tracing paper coated with a layer comprising about I part of leucomalachite green and 5 parts of n-butyl/isobutylmethacrylate /50 copolymer resin on its surface. The zinc oxide particles are coated with a compound capable of influencing a pH change for the above coated sheet as follows: about 4 parts of malonic acid is dissolved in 100 parts of methanol; 4 parts of zinc oxide are added to this solution and the zinc oxide thus coated with malonic acid is filtered and dried. The coated zinc oxide particles are dispersed in Sohio 3440 kerosene fraction as in Example I employing about 20 parts of coated zinc oxide particles in 100 parts by weight carrier liquid. The imaging process is carried out as in Example I providing a positive image on the surface of the lecomalachite green coated sheet. The sheet bearing the image is then heated to fix the image and cause reaction to take place providing a green image.

EXAMPLE X In this example, the roller electrode contains a sheet thereon of 85 g/m tracing paper coated with a layer comprising. about 1 part of N,N-dimethyl-pphenylenediamine and 5 parts of the polyamide resin employed in Example IV on its surface. The zinc oxide particles are coated with a compound capable of releasing an oxidizing agent for the above coated sheet as follows: about 1 part of benzoyl peroxide is dissolved in 100 parts of methanol; 4 parts of zinc oxide are added to this solution and the zinc oxide thus coated with benzoyl peroxide is filtered and dried. The coated zinc oxide particles are dispersed in Sohio 3440 kerosene fraction as in Example I employing about 20 parts of coated zinc oxide particles in 100 parts by weight carrier liquid. The imaging process is carried out as in Example I providing a positive image on the surface of the N,N-dimethyl-p-phenylenediamine sheet. The sheet bearing the image is then heated to fix the image and cause reaction to take place providing a bluish image.

EXAMPLE XI In this example, the roller electrode contains a sheet thereon of g/m tracing paper coated with a layer comprising about 1 part of silver behenate and 5 parts of the polyamide resin employed in Example IV on its surface. The zinc oxide particles are coated with a com pound capable of chromogenic reaction for the above coated sheet as follows: about 1 part of 1-phenyl-3- pyrazolidinone is dissolved in parts of methanol; 4 parts of zinc oxide are added to this solution and the zinc oxide thus coated with a 1-phenyl-3- pyrazolidinone is filtered and dried. The coated zinc oxide particles are dispersed in Sohio 3440 kerosene fraction as in Example I employing about 20 parts of coated zinc oxide particles in The 100 parts by weight carrier liquid. The imaging process is carried out as in Example 1 providing a positive image on the surface of the silver behenate coated sheet. The sheet bearing the image is then heated to fix the image and cause reaction to take place providing a brown image.

EXAMPLE XII providing In this example, the roller electrode contains a sheet thereon of 85 g/m tracing paper coated with a layer comprising about 1 part of 8-hydroxy-l ,2,3,,4- tetrahydroquinoline and 5 parts of cellulose acetate bu tyrate on its surface. The zinc oxide particles are coated with a compound capable of chromogenic reaction for the above coated sheet as follows: about 1 part of ferric stearate is dispersed in 100 parts of methanol; 4 parts of zinc oxide are added to this dispersion and the zinc oxide thus combined with ferric stearate is filtered and dried. The coated zinc oxide particles are dispersed in Sohio 3440 kerosene fraction as in Example I employing about 20 parts of coated zinc oxide particles in 100 parts by weight carrier liquid. The imaging process is carried out as in Example I providing a positive image on the surface of the 8-hydroxy-l,2,3,4- tetrahydroquinoline coated sheet. The sheet bearing the image is then heated to fix the image and cause reaction to take place providing a purple gray image.

EXAMPLE XIII In this example, the roller electrode has a sheet of 85 g/m tracing paper coated with a layer comprising about 1 part of silver behenate and 5 parts of the polyamide resin employed in Example IV on its surface.

The zinc oxide particles are coated with a compound capable of chromogenic reaction for the above coated sheet as follows: about 1 part of pyrogallol is dissolved in 100 parts of methanol; 4 parts of zinc oxide are EXAMPLE XIV Example VIII is repeated except that the amount of silver behenate in the polyamide resin coating on paper is replaced by the same amount of p-phenylenediamine and the zinc oxide is coated with the same amount of tetrachloroquinone in place of the dithiooxamide.

A legible, positive brown image is obtained on the coated sheet after heating.

EXAMPLE XV Example XIII is repeated except that the amount of silver behenate in the polyamide resin coating on paper is replaced by the same amount of nnitrosodiphenylamine. The sheet bearing the image is then heated to fix the image and cause reaction to take place providing a brown image.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An imaging method comprising the steps of:

a. providing a layer of an imaging suspension comprising finely divided chromogenic particles in an electrically insulating liquid between a pair of electrodes at least one of which is at least partially transparent, each of said particles comprising an electrically photosensitive pigment;

b. providing an image receiving layer comprising a co-reactant for the chromogenic material of said particle;

c. applying an electrical field across said suspension layer and exposing said layer to an imagewise pattern of activating electromagnetic radiation through said transparent electrode, wherein an image is formed on said image receiving layer; and

d. chromogenically reacting the chromogenic mate rial of the particles with the co-reactant of the receiving layer.

2. The method as defined in claim 1 wherein said particles and said image receiving layer react in the presence of an alkaline media and step (d) includes applying ammonia vapor to said image receiving layer.

3. The method as defined in claim 1 wherein said par-v ticles and said image receiving layer react in the presence of heat and step ((1) includes heating said image receiving layer.

4. The method as defined in claim 1 wherein said image receiving layer is a thermoplastic.

S. The method as defined in claim 1 wherein said image receiving layer is a diazo sheet.

6. The method as defined in claim 5 wherein said particles are coated with a diazo color coupler.

1 7. The method as defined in claim 1 wherein said particles comprise zinc oxide.

8. The method as defined in claim 1 wherein said image receiving layer comprises a material selected from the group consisting of polyvinyl chloride and a copolymer of vinylidene chloride and acrylonitrile.

9. The method as defined in claim 1 wherein said image receiving layer is transparent and said suspension layer is exposed to said imagewise pattern of radiation through said image receiving layer. 

1. AN IMAGING METHOD COMPRISING THE STEPS OF: A. PROVIDING A LAYER OF AN IMAGING SUSPENSION COMPRISING FINELY DIVIDED CHROMOGENIC PARTICLES IN AN ELECTRICALLY INSULATING LIQUID BETWEEN A PAIR OF ELECTRODES AT LEAST ONE OF WHICH IS AT LEAST PARTIALLY TRANSPARENT, EACH OF SAID PARTICLES COMPRISING AN ELECTRICALLY PHOTOSENSITIVE PIGMENT; B. PROVIDING AN IMAGE RECEIVING LAYER COMPRISING A COREACTANT FOR THE CHROMOGENIC MATERIAL OF SAID PARTICLE; C. APPLYING AN ELECTRICAL FIELD ACROSS SAID SUSPENSION LAYER AND EXPOSING SAID LAYER TO AN IMAGEWISE PATTERN OF ACTIVATING ELECTROMAGNETIC RADIATION THROUGH SAID TRANSPARENT ELECTRODE, WHEREIN AN IMAGE IS FORMED ON SAID IMAGE RECEIVING LAYER; AND D. CHROMOGENICALLY REACTING THE CHROMOGENIC MATERIAL OF THE PARTICLES WITH THE CO-REACTANT OF THE RECEIVING LAYER.
 2. The method as defined in claim 1 wherein said particles and said image receiving layer react in the presence of an alkaline media and step (d) includes applying ammonia vapor to said image receiving layer.
 3. The method as defined in claim 1 whereIn said particles and said image receiving layer react in the presence of heat and step (d) includes heating said image receiving layer.
 4. The method as defined in claim 1 wherein said image receiving layer is a thermoplastic.
 5. The method as defined in claim 1 wherein said image receiving layer is a diazo sheet.
 6. The method as defined in claim 5 wherein said particles are coated with a diazo color coupler.
 7. The method as defined in claim 1 wherein said particles comprise zinc oxide.
 8. The method as defined in claim 1 wherein said image receiving layer comprises a material selected from the group consisting of polyvinyl chloride and a copolymer of vinylidene chloride and acrylonitrile.
 9. The method as defined in claim 1 wherein said image receiving layer is transparent and said suspension layer is exposed to said imagewise pattern of radiation through said image receiving layer. 